Alcohols having a double bond in the alpha position are conventionally converted into ketones in the presence of inorganic oxidizing agents (e.g. KMnO4, OsO4, H2SO4/H2CrO4). In particular, it is known to convert an alcohol of the formula (I) into a ketone of the formula (II) in this manner:
wherein the radicals R1, R2 independently of one another can be alkyl, alkenyl, cycloalkyl or aryl. Alcohols of the formula (I) are obtained from natural sources in some cases, but are also accessible by synthesis.
WO 91/09852 describes a two-stage process for the preparation of sclareolide (also (−)-norlabdan oxide) from sclareol, in which in a first stage an oxidative degradation of sclareol in the presence of ruthenium salts or potassium permanganate takes place, and in a second stage the intermediate product formed is oxidized with peracid and/or peracid salts to give sclareolide.
Barton et al. (Tetrahedron Letters, 1994, 35(32), 5801) describe a further synthesis set-up for the preparation of sclareolide starting from sclareol, and in particular by oxidative reaction of the starting substance with a mixture of OsO4/NalO4.
The oxidizing agents used in conventional processes are a disadvantage because of their toxicity to man and the environment and their ease of handling being made difficult as a result. This disadvantage in particular makes the industrial reaction of alcohols having a double bond in the alpha position difficult.
Attempts have therefore been made to modify these processes, and in particular to use novel oxidizing agents. Thus, EP 0 822 191 A1 and Fekih et al. (J. Soc. Chim. Tunisie, 2001, 4(9), 909) each describe two-stage processes for the preparation of sclareol oxide from sclareol by ozonolysis:

In a first stage, the allyl alcohol group of the sclareol is converted into the corresponding ozonide by addition of ozone. In a second stage, the ozonide is then converted into the desired sclareol oxide by working up with alkaline H2O2. The reaction can be carried out in various organic solvents, such as methylene chloride, methanol or ethanol. In the reaction, however, large amounts of the highly reactive ozonide are obtained in the first step, so that considerably safety precautions are necessary for carrying out the reaction. In particular, an efficient cooling is required in order to be able to carry out the reaction safely. These disadvantages are important in particular in an industrial reaction.